| Electronics > Repair |
| E4407B Tracking Generator Repair |
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| smgvbest:
--- Quote from: analogRF on September 25, 2020, 02:41:55 pm --- --- Quote from: Jay_Diddy_B on September 25, 2020, 02:13:36 pm ---Hi, The U2000H Power meter will be very useful when tracking this problem down. (Attachment Link) The output amplitude of the TG is proportional to the product of the signal levels at A and B. The signal level at A should be fixed at +16dBm. The signal level at B should vary depending on the setting of the TG output level. It is the 'fine' control. The coarse steps come from the step attenuator. Can you use the U2000H and measure the signal levels at A and B? Jay_Diddy_B --- End quote --- looking at the circuit, I don't think the final amplitude is controlled by the amplitude of 600MHz. Rather I think it is controlled by the Hittite variable attenuator just before the main mixer. The 600MHz goes to a mixer directly and then through quite a bit of processing including what I think is a frequency doubler and then reaches the variable attenuator just before the mixer. Maybe -4.5 to -11dBm only indicates the acceptable range for 600MHz? or could it be that both the 600MHz amplitude and the Hittite chip together control the RF amplitude? What I still dont quite get is that what they are mixing with the 600MHz? It looks like a free running oscillator!? with no locking?! They need to create a 3.92GHz out of the 600MHz but it should be a very stable and locked signal...i cannot see how it is.... --- End quote --- On the other side of the A2A2 board is a component marked 40 / 0410-2110 / 9251 is 0410-2110 a freq range? see pics would the 600Mhz mix with that, then later mix with the LO There is a TUNE signal coming in on J1 from the control board |
| suj:
--- Quote from: smgvbest on September 25, 2020, 04:05:26 pm ---On the other side of the A2A2 board is a component marked 40 / 0410-2110 / 9251 is 0410-2110 a freq range? --- End quote --- Maybe it's a heated quartz resonator? Or another type of oscillator. Maybe the mixer mixes the 6th harmonic of the 600 MHz signal with the signal of this oscillator? Then strong filtering. In my opinion this part of the system must provide a signal with a constant frequency of approximately 3.92 GHz. The 6th harmonic of 600 MHz is 3.6 GHz. 320 MHz is missing to 3.92 GHz. A lot for a quartz resonator ... See the service manual for the 1.5 GHz tracking generator block diagram. Some 800 MHz oscillator is used there. Maybe it's something similar? EDIT. It's a bit of a mystery to me. The mixer is up to 1 GHz. I can't see the PLL closing anywhere. The 600 MHz signal is synthesized, but for this oscillator (if it's an oscillator) I don't see dividers or phase detector. |
| smgvbest:
Something though is getting a tuning signal from the A2A1 board as well as osc-pwr. So there is a oscillator there somewhere and it gets tuned I’m going to have to get a SMB connector as well as 10 pin extension cables made up before I can do some measurements. The boards fir the A2A2 are stacked tightly. I do have one of the thermo cams for my iPhone but need to see the components. |
| KE5FX:
That looks like a big inductor, usually something you'd see in an HP switching supply. 0410-2110 is the HP part #. Odd that it has polarity markings, though. |
| smgvbest:
And it’s got 3 terminals |
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